Functions and collections · Lesson 6 of 21

Functions

Defining and returning, default arguments, and overloading.

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A function is named code you call when needed. In C++ you write the type it returns before the name (int, double, or void for nothing) and the type of every parameter.

C++

#include <iostream>
#include <string>

double average(int total, int count) {
    if (count == 0) return 0;
    return static_cast<double>(total) / count;
}

void greet(const std::string& name, const std::string& greeting = "Welcome") {
    std::cout << greeting << ", " << name << "!\n";
}

int main() {
    std::cout << average(17, 4) << "\n";
    greet("Omar");
    greet("Nour", "Good morning");
    return 0;
}

greeting has a default value, so leaving it out gives "Welcome". Defaults must come last in the parameter list.

Overloading: same name, different types

C++

#include <iostream>
#include <string>

int twice(int x) { return x * 2; }
double twice(double x) { return x * 2; }
std::string twice(const std::string& s) { return s + s; }

int main() {
    std::cout << twice(21) << "\n";
    std::cout << twice(1.25) << "\n";
    std::cout << twice(std::string("ha")) << "\n";
    return 0;
}

twice(21)

the compiler sees the type: int

picks int twice(int)

The choice happens at compile time, not while running.

Complete the code

Complete the function that returns the larger of two numbers.

#include <iostream>
 larger(int a, int b) {
     a > b ? a : b;
}
int main() { std::cout << larger(3, 8) << "\n"; }

Exercise

Write bool isPrime(int n) and use it to print the primes from 2 to 30 on one line, separated by spaces.

Expected output: 2 3 5 7 11 13 17 19 23 29

C++

#include <iostream>

bool isPrime(int n) {
    
}

int main() {
    for (int i = 2; i <= 30; i++) {
        if (isPrime(i)) std::cout << i << " ";
    }
    std::cout << "\n";
    return 0;
}

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